Not applicable.
The invention relates to a method for using water hydraulics in a paper or board machine, in particular in applications requiring lubrication and in the like in which an operating medium is subjected to pressure.
Conventionally, in paper and board machines, oil is used in several applications as an operating liquid, in cooling systems, in bearing arrangements, etc. The apparatus must be tightly encased to prevent the drawbacks of oil leakages in order that oil should not be allowed to damage the product which is being manufactured, such as paper or board, or to contaminate the devices situated in the surroundings. Moreover, when oil gets into the environment, for example, with waters discharging from a mill, it is very harmful because of the pollution of the environment. Considerable amounts of heat are generated in different bearing applications of rolls and it is therefore necessary to use in these bearing applications large cooling systems, in which lubricating oil is most commonly cooled by means of water. Possible oil leakages often get into the environment and, as already stated above, the disposal of oil causes substantial loadings to the environment. Additionally, hot oil is a risk factor in terms of fire safety. When thinking, for example, of the rolls which are used in paper machines and which are loaded with hydraulic oil and journalled with slide bearings, the hydraulic medium demand per roll is substantial. As an example, it may be mentioned that about 10 to 12 m3 of hydraulic oil is needed for one deflection-compensated roll loaded with hydraulic oil. When one machine includes a considerable number of such rolls, the paper mill has to keep a very large stock of hydraulic oil.
Electricity is used as driving power in several devices, in which connection it is necessary to set special requirements for these electric motors because of the humid surroundings. In addition, in some equipment in paper machines, air is used as driving power, which again requires a separate pneumatic system of its own. When it is necessary to use simultaneously several different types of driving power and to build several different operating medium lines, to encase devices, to construct special arrangements because of fire safety, etc., these actions cause, of course, considerable costs, and further this kind of solutions require an abundance of space to place the equipment in machines. Today, attempts are being made to achieve durable arrangements which protect the environment, are economical and take little space, in which connection more and more attention is being paid to the use of environmentally friendly and economical water as driving power instead of other operating mediums.
With respect to the prior art relating to water hydraulic systems, reference is made, for example, to Finnish patent 76 409 which describes journal bearings which are suitable for rotating transfer rolls and spreader rolls and in which water is used as lubricant. The use of water is suitable for this kind of system because the operating medium is not subjected to high pressure in the system. The system described in this Finnish patent cannot be applied to a system under high pressure.
U.S. Pat. No. 4 167 964 describes an apparatus intended for rolling of metal, which apparatus uses rolls loaded with a pressure medium. In the case described in this publication, water is used as the pressure medium. In addition to pressurization, water is used in the system for lubrication and for cooling. In spite of high working pressures, the use of water is feasible in the system because a very high flow rate of water is used in addition to pressurization. If the used flow of water were slight, it could not be used for pressurization because of the low viscosity of water.
Finnish patent application No. 942616 discloses a prepress for a paper web, in particular a shoe press, in which water is used as the operating liquid in a loading shoe. Water serves in the system simultaneously as a lubricating medium and as a medium producing a loading pressure. The use of water also in this arrangement is possible because the loading pressures used are not very high and, in addition, the flow of the loading medium is high at the same time. In that connection, the low viscosity is not too detrimental from the point of view of the use of the arrangement.
The aim of the present invention is to provide a method which allows the use of water hydraulics in a paper and board machine also in applications in which the operating medium is subjected to a considerable pressure. With a view to achieving this aim, the invention is mainly characterized in that some chemical used in the stock system of the process is mixed with the water used in water hydraulics before the water is passed to a site of application in order to raise the viscosity of the water and chemical mixture to a level required by the site of application, the water and chemical mixture is passed to the site of application and circulated through the same at least once, after which said water and chemical mixture is recovered and passed to the stock system of the process as diluted to a suitable concentration.
As a special application of the invention it is proposed that the method is applied to roll hydraulics, in particular to the lubrication of rolls journalled with slide bearings and/or to the pressurization and lubrication of the loading elements of hydraulically loaded rolls and the like.
Thus, in the method according to the invention, attempts are made to replace with water hydraulics in particular such oil hydraulics which is intended to produce remarkably high pressure levels. Slide bearings of rolls, internally loaded deflection-compensated rolls, band rolls, such as long-nip rolls and the like may be mentioned as examples of these. The use of water hydraulics provides substantial benefits over previous arrangements, one of the most important benefits being the fact that it is environmentally friendly. In respect of the operating medium, the system is very economical because the hydraulic oils conventionally used are relatively expensive. A significant advantage is also that the operating medium in water hydraulics is incombustible. If there occur any leakages in the system, these leakages will not contaminate its surroundings. This means that even large leakages will not cause problems, but in most cases the leakage waters can be discharged directly into the drain or into a treatment system of the circulation water of the paper machine. Owing to the low viscosity of water, no large-diameter pipes are needed in the system. Relatively long pipe lines are also possible. When changing over from oil hydraulics to water hydraulics, substantial alterations need not necessarily be made in the pipe lines especially if the pipe lines of oil hydraulics have already been made of an acid-proof material. The use of a water hydraulic system does not involve the air separation problem similar to that of oil hydraulic systems. A water hydraulic system does not require large storage tanks of the kind needed in oil hydraulic systems. In some instances, in water hydraulic systems it would also be possible to use sea water as the medium. The other advantages and characteristic features of the invention will come out from the following detailed description of the invention.